To assist physicians, surgeons and dentists in observing smaller body parts, various telescopes or loupes are commercially available. These loupes are typically either of the Galilean or Keplerian design types, which may be pivotally mounted on eyeglass frames or fixed into the lens.
Keplerian optics design is typically used for higher magnification applications, and image-rotating components such as a pair of roof Pechan prisms is typically utilized to form an erect image. Such prisms are relatively heavy, and are located in the optical path in between the objective and the eyepiece.
A typical prior-art telescopic loupe based upon a Keplerian optical system is shown in FIG. 1. The objective lens shown generally at 102, the eyepiece lens is shown generally at 104, and the image-rotator (prisms) is shown generally at 106. The objective forms an image plane 110 which is outside the image-rotator 106 and the eyepiece relays the image to the entrance pupil of the eye 116. The objective 102 can be mounted on a threaded ring, so that it can be moved forward and backward to adjust for a working distance. Item 112 is a replaceable transparent protective cap, and item 114 is an optional prescription lens.
With this particular design, the distance between the cap 112 and the back of the eyepiece 104 is over 54 mm, and the distance from the eyepiece to the eye is another 16 mm, resulting in the design having a length of over 70 mm. The length and weight of the components in such a design may result in an undesirable cantilever effect, particularly when the telescopes are mounted through lenses or supported on eyeglass frames as part of a surgical/medical/dental loupe configuration.